In recent years, inland sand unloading vessels have attracted widespread attention due to their advantages of flexible and quick cargo unloading performance. However, the instability of such vessels also has become increasingly prominent. Furthermore, due to large water coverage and rich waterway resources in China, inland sand unloading vessels have been widely applied and this industry is booming. However, the conveyor boom of a conventional self-unloading vessel may have a length up to 40 m, but it cannot be retracted, resulting in low stability and high safety hazard. For example, since accidents frequently occur in the conventional overhung belt racks, the insurance for belt racks had been refused by insurance companies in China.
Therefore, to solve the technical difficulty in retracting conveyor booms, many solutions have been proposed in China, such as stretchable and retractable conveyor booms, rotary conveyor booms and folding conveyor booms.
The published Inventive Patent No. 201610594201.8, entitled “SELF-ADAPTIVE INTEGRALLY-OVERTURNED CONVEYOR”, provided a conveying solution in which a two-drum winch and an integral trussed boom are used and the conveyor boom is pulled by the two-drum winch to be folded. This solution solves occupation of the space of the hull to some extent; the integral overturning mode is simpler and more convenient than the folded overturning mode; and during the sand unloading, the boom is higher in safety. However, due to the use of the integral trussed boom that is fixed in length, the conveying distance is not adjustable. Although the integral overturning mode is simpler and more convenient than the folded overturning mode, the overturned conveyor arm is suspended, not firmly fixed, resulting in high safety hazard.
The published Inventive Patent No. 201610728114.7, entitled “CONVEYOR WITH STRETCHABLE AND RETRACTABLE CONVEYOR ARM”, provided a solution in which a multi-stage hydraulic cylinder and a scissor fork mechanism are used, and the retraction of the scissor fork mechanism is realized by the multi-stage hydraulic cylinder to thus make the conveyor arm stretchable and retractable. This solution realizes, to some extent, small influence to the balance of the hull by the stretch and retraction of the conveyor arm, large stretchable distance, high stretch and retraction efficiency, stable operation, and high safety. In contrast, compared with the scissor fork mechanism, the multi-bar linkage mechanism is more stable in operation, larger in the stretchable distance, and safer than the multi-stage hydraulic cylinder because the conveyor boom is unfolded in a unit of multi-bar linkage mechanisms; no tensioning mechanism is required; and it is more convenient for production and assembly.